An ultrametric preserving function f is said to be strongly ultrametric preserving if ultrametrics d and f degrees d define the same topology on X for each ultrametric space (X, d). The set of all strongly ultrametric preserving functions is characterized by several distinctive features. In particular, it is shown that an ultrametric preserving f belongs to this set iff f preserves the property to be compact. (c) 2024 Elsevier B.V. All rights reserved.